The present invention relates to a method and apparatus for burning carbonaceous material in a fluidized bed reactor that includes: a bottom portion; a top portion; wall cooling surfaces; a recirculation or return system that includes at least one labyrinth separator which serves for the return of separated-off solid material to the bottom portion and is provided with staggered beams that have an essentially U-shaped cross-sectional configuration and are open toward a rising flow of flue gas; a fuel supply, a fluidizing air supply, and a secondary air supply in the bottom portion; and at least one dust separator disposed downstream of the at least one labyrinth separator.
WO 83/03294 discloses a boiler having a circulating fluidized bed; the fuel is introduced into a fluidized bed reactor which is free of baffles and has wall cooling surfaces. The flue gas, which is charged with solids, is deflected through 90.degree. and leaves the fluidized bed reactor at the top end thereof and flows along a horizontal flue-gas line to a descending flue. The gas is then again deflected substantially through 90.degree. and enters a rising flue in which convective heating surfaces are disposed.
A non-centrifugal mechanical separator in the form of a labyrinth separator is disposed in the connecting line and in the descending flue. The separator elements in the connecting line extend substantially vertically, and the solid material separated by them is conveyed to a storage chamber disposed between the fluidized bed reactor and the descending flue. The separator elements in the descending flue slope down towards the storage chamber, so that the solids separated by them can likewise be supplied thereto. The bottom end of the storage chamber is connected by a number of "L-valves" to the bottom portion of the fluidized bed reactor, so that the solids deposited in the storage chamber can be recirculated in a controlled manner, by means of a fluidizing device associated with the L-valve, to the bottom region of the reactor above the valve tray therein. In WO 83/03294, as in the present specification and claims, the term "labyrinth separator" means a separator where separation occurs through gravity and/or momentum, i.e. without centrifugal force. In the known boiler, staggered lines or chutes are used that extend substantially transverse to the flow of flue gas and that open toward it in a substantially U-shape.
The disadvantage of the known boiler is that the storage chamber, which is disposed outside the reactor, together with one or more L-valves connected downstream, are necessary for the recirculation system, which is external; i.e. separate ash lines and corresponding conveying and regulating equipment are needed.
It is therefore an object of the present invention to provide a method where it is no longer necessary to remove the solids from the fluidized bed reactor.